The embodiments disclosed herein relate generally to electrophotographic imaging members and more specifically to overcoats for electrophotographic imaging members.
Electrophotographic imaging members are photoreceptors that typically include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the dark so that electric charges can be retained on its surface. Upon exposure to light, the charge is dissipated.
One type of electrophotographic imaging member is a multi-layered device that comprises a conductive layer, an optional blocking layer, an optional adhesive layer, a charge generating layer, and a charge transport layer. The charge generating layer and charge transport layer can be combined into a single layer. One approach to achieving longer photoreceptor life is to form a protective overcoat on the imaging member. This overcoat layer usually is designed to resist image deletion and wear, while keeping transporting charges. Furthermore, application of this overcoat should not damage underlying layers of the photoreceptor. Additionally, the pot life of the coating solutions must be sufficiently long that the coating can be applied economically.
Known overcoats for imaging members are formed from hydrolyzed silica gel, crosslinked silicone or polyamides. Typical coatings are thin, usually less than 5 microns, in order to provide some degree of improvement in mechanical properties without substantially reducing the electrical properties of the charge transport layer.
Commonly assigned U.S. Pat. No. 6,835,515, the contents of which are incorporated herein by reference, describes a long potlife, low temperature cure overcoat for low surface energy electrophotographic imaging members. The overcoat is formed from a composition that includes a hole transport material such as a polyhydroxytriaryl amine, a cross-linkable film forming binder having at least one functional group that is reactive with isocyanate, a blocked isocyanate cross-linking agent, and a solvent having a boiling point equal to or below the deblocking temperature. The blocked isocyanate usually is the reaction product of an isocyanate and a blocking agent.
Commonly assigned U.S. Pat. No. 5,436,099 discloses an electrophotographic imaging member including a substrate, a charge generating layer, a charge transport layer, and an overcoat layer. The overcoat layer comprises a hole transporting hydroxy arylamine compound having at least two hydroxyl functional groups, hydroxy terminated siloxane, and a polyamide film forming binder capable of forming hydrogen bonds with the hydroxyl functional groups of the hydroxy arylamine compound and the hydroxy terminated siloxane.
It would be useful to develop additional photoreceptor overcoats with low surface energy and excellent wear resistance.